If you had a party at home for your 3 year old, did you plan activities or did you just set out some things for them to play with?

I'm thinking of inviting some daycare kids for M's party and don't want to go crazy. We are only inviting older 2/young 3 year olds to the party. I was thinking it would be enough if we open the sandbox, fill up the blow-up pool, put out the colored rice bin and put chalk and bubbles on the patio. That's enough, right? Any other free/very cheap ideas?